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单例模式（Singleton Pattern）：</p> <ul><li>保证一个类仅有一个实例（只生成唯一的实例对象）</li> <li>并且提供一个访问它的全局访问点。</li></ul> <p>2）项目实践中场景</p> <ul><li>比如多线程编程中，要是需要通过该使用socket资源，但是明显的多次初始化socket会浪费资源，所以我们的做法是只初始化一次</li> <li>在Java中，servlet环境中，我们需要共享同一个资源或者操作同一个对象</li></ul> <h2 id="二、类图如下"><a href="#二、类图如下" class="header-anchor">#</a> 二、类图如下</h2> <h2 id="三、实现代码"><a href="#三、实现代码" class="header-anchor">#</a> 三、实现代码</h2> <p>我们由单例模式的概念，可以抽象出我们在面向对象程序设计的时候需要这么做</p> <blockquote><ul><li>1）构造函数私有化</li> <li>2）提供一个全局访问点（用全局的静态方法实现）</li> <li>3）在列中定义</li></ul></blockquote> <ul><li>让<strong>构造函数为 private</strong>，这样该类就不会被实例化</li></ul> <p>根据什么时候new单例的情况，可以分为懒汉式和饿汉式</p> <h3 id="单线程——懒汉式"><a href="#单线程——懒汉式" class="header-anchor">#</a> 单线程——懒汉式</h3> <div class="language-cpp line-numbers-mode"><pre class="language-cpp"><code><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span><span class="token string">&lt;iostream&gt;</span></span>
<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>

<span class="token keyword">class</span> <span class="token class-name">Singelton</span>
<span class="token punctuation">{</span>
	<span class="token keyword">private</span><span class="token operator">:</span>
		<span class="token keyword">static</span> Singelton <span class="token operator">*</span> ptr<span class="token punctuation">;</span>
		<span class="token keyword">static</span> <span class="token keyword">int</span> count<span class="token punctuation">;</span>
	<span class="token comment">//构造函数注意是：private</span>
		<span class="token function">Singelton</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			ptr<span class="token operator">=</span><span class="token constant">NULL</span><span class="token punctuation">;</span>
			count<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>
			cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;调用构造函数&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	
	<span class="token keyword">public</span><span class="token operator">:</span>
		<span class="token comment">//获取单例的全局访问点，获取单例的接口 </span>
		<span class="token keyword">static</span> Singelton <span class="token operator">*</span> <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token constant">NULL</span><span class="token operator">==</span>ptr<span class="token punctuation">)</span>
			<span class="token punctuation">{</span>
				ptr<span class="token operator">=</span><span class="token keyword">new</span> Singelton<span class="token punctuation">;</span>
			<span class="token punctuation">}</span> 
			<span class="token keyword">return</span> ptr<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		
		<span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;cout=&quot;</span><span class="token operator">&lt;&lt;</span>count<span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
		<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token comment">//懒汉式的地方：并不创建单例对象 </span>
Singelton <span class="token operator">*</span> Singelton<span class="token operator">::</span>ptr<span class="token operator">=</span><span class="token constant">NULL</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> Singelton<span class="token operator">::</span>count<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>


<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
	cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;单线程——懒汉式&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span>
	
	<span class="token comment">//调用getInstance，当单例不存在则new，存在则不new</span>
	<span class="token comment">//保证了一个单例 </span>
	Singelton <span class="token operator">*</span> p1<span class="token operator">=</span><span class="token class-name">Singelton</span><span class="token operator">::</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	Singelton <span class="token operator">*</span> p2<span class="token operator">=</span><span class="token class-name">Singelton</span><span class="token operator">::</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	
	<span class="token keyword">if</span><span class="token punctuation">(</span>p1<span class="token operator">!=</span>p2<span class="token punctuation">)</span> 
	<span class="token punctuation">{</span>
		cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;不是同一个对象&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
	<span class="token punctuation">}</span>
	<span class="token keyword">else</span>
	<span class="token punctuation">{</span>
		cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;是同一个对象&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
	<span class="token punctuation">}</span>
	
	p1<span class="token operator">-&gt;</span><span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	p2<span class="token operator">-&gt;</span><span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	
	<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br></div></div><h3 id="单线程——饿汉式："><a href="#单线程——饿汉式：" class="header-anchor">#</a> 单线程——饿汉式：</h3> <div class="language-cpp line-numbers-mode"><pre class="language-cpp"><code><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span><span class="token string">&lt;iostream&gt;</span></span>
<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>

<span class="token keyword">class</span> <span class="token class-name">Singelton</span>
<span class="token punctuation">{</span>
	<span class="token keyword">private</span><span class="token operator">:</span>
		<span class="token keyword">static</span> Singelton <span class="token operator">*</span> ptr<span class="token punctuation">;</span>
		<span class="token keyword">static</span> <span class="token keyword">int</span> count<span class="token punctuation">;</span>
		
		<span class="token function">Singelton</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			ptr<span class="token operator">=</span><span class="token constant">NULL</span><span class="token punctuation">;</span>
			count<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>
			cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;调用构造函数&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	
	<span class="token keyword">public</span><span class="token operator">:</span>
		<span class="token comment">//获取单例的全局访问点，获取单例的接口 </span>
		<span class="token keyword">static</span> Singelton <span class="token operator">*</span> <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			
			<span class="token keyword">return</span> ptr<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		
		<span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
		<span class="token punctuation">{</span>
			cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;cout=&quot;</span><span class="token operator">&lt;&lt;</span>count<span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
		<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token comment">//饿汉式的地方：无论你会不会用到，先给你创建了单例对象 </span>
Singelton <span class="token operator">*</span> Singelton<span class="token operator">::</span>ptr<span class="token operator">=</span><span class="token keyword">new</span> Singelton<span class="token punctuation">;</span>
<span class="token keyword">int</span> Singelton<span class="token operator">::</span>count<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>


<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
	cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;单线程——饿汉式&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span>
	
	
	Singelton <span class="token operator">*</span> p1<span class="token operator">=</span><span class="token class-name">Singelton</span><span class="token operator">::</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	Singelton <span class="token operator">*</span> p2<span class="token operator">=</span><span class="token class-name">Singelton</span><span class="token operator">::</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	
	<span class="token keyword">if</span><span class="token punctuation">(</span>p1<span class="token operator">!=</span>p2<span class="token punctuation">)</span> 
	<span class="token punctuation">{</span>
		cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;不是同一个对象&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
	<span class="token punctuation">}</span>
	<span class="token keyword">else</span>
	<span class="token punctuation">{</span>
		cout<span class="token operator">&lt;&lt;</span><span class="token string">&quot;是同一个对象&quot;</span><span class="token operator">&lt;&lt;</span>endl<span class="token punctuation">;</span> 
	<span class="token punctuation">}</span>
	
	p1<span class="token operator">-&gt;</span><span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	p2<span class="token operator">-&gt;</span><span class="token function">Singelton_Print</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	
	<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br></div></div><h2 id="四、多线程代码"><a href="#四、多线程代码" class="header-anchor">#</a> 四、多线程代码</h2> <div class="language-txt line-numbers-mode"><pre class="language-text"><code>### 1）Windows下多线程

### 2）Linux下多线程
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h2 id="参考资料"><a href="#参考资料" class="header-anchor">#</a> 参考资料</h2> <ul><li>国外，<a href="https://refactoringguru.cn/design-patterns" target="_blank" rel="noopener noreferrer">设计模式网站<svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg></a></li></ul></div> <div class="page-edit"><!----> <!----></div> <!----> </div> <!----></div></div>
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